Retinitis pigmentosis is a disease of the retina that has many different pathological manifestations. Notably, it not only causes restriction of a patient's field of vision, but also increased difficulty in adapting to the dark and to penumbra, when it affects the peripheral zones of the retina. Generally speaking, this is because the peripheral zones accommodate a greater part of the rod cells that make vision in penumbra and perception of movement in the lateral zones possible. Alternatively or concurrently, retinitis pigmentosis may lead to loss of central vision, when the cone cells are the ones that are affected by the disease and, thereby, undergo deterioration. The rate at which the illness progresses varies from one patient to another. Overall, however, retinitis pigmentosis is an insidious disease that most often manifests itself in youth, especially children.
The cause(s) of this infirmity are presently unknown and there is not yet a cure. The only information known for certain about the disease concerns its possible genetic origin. More particularly, retinitis pigmentosis is believed to be passed, in part, by heredity from generation to generation, following mechanisms known to geneticists. Most forms of retinitis pigmentosis are hereditary and three transmission modalities have been identified thus far: dominantly autosomal, recessively autosomal and X-linked or bound by sex.
The main symptoms of the disease are crepuscular and nocturnal blindness, i.e., difficulty of seeing when lighting conditions are poor, and problems adaptating from well-lit to dark environments or vice versa. This phenomenon is due to the fact that, at least in a majority of cases, attack in the early development phases of the illness is concentrated on the rod cells. Other common symptoms are a reaction to excessively strong light, a gradual narrowing of the visual field, which manifests itself in the form of difficulty in perceiving objects situated to either side of the patient, or stumbling over steps or other low obstacles, eventually resulting in complete blindness.
The course followed by the illness is of extremely variable duration, but is always gradual and ultimately leads to disability. In the greater part of cases, however, the symptoms described previously become aggravated, the visual field becomes more and more restricted and eventually closes completely. Other complaints tend to appear, dazzlement being among them, as well as the inability to distinguish colors, and a particular form of cataract. In many cases, the final outcome is, unfortunately, total blindness.
In diagnosing retinitis pigmentosis, it is common to rely on tests such as examination of the fundus of the eye, examination of the visual field, electroretinograms, fluorangiography, and visus examination:                the fundus of the eye is examined to assess the condition of the retina and to look for the presence of pigment spots on the retinal surface characteristic of the illness, which assume an “osteoblast-like” appearance. It is noted that some rare forms of retinitis pigmentosis are not characterized by spots on the fundus of the eye, though they present the same symptoms otherwise;        examination of the visual field makes it possible to evaluate the sensitivity of various parts of the retina to light stimuli. It is considered particularly useful to have objective documentation of the difficulty in visual perception experienced by the patient;        an electroretinogram (ERG) records the electrical activity of the retina in response to particular light stimuli, thereby enabling the functionality of the two different types of photoreceptors (i.e. cone cells and rod cells) to be evaluated. The electroretinogram is very important for diagnosing retinitis pigmentosis, because—even when the illness is in its initial stages—the resulting trace almost always is either very flat or absent altogether;        fluorangiography is performed by intravenous injection of a fluorescent substance and subsequent photography of the retina at different times. As a result of blood circulation, the fluorescent substance arrives at the retina, where it colours the arteries, the capillaries and the veins, rendering them and the functional state of their walls visible;        visus examination allows visual acuity to be evaluated and involves the patient's reading of letters having different sizes at a distance of about three meters.        
Although retinitis pigmentosis was identified and classified as a disease more than fifty (50) years ago, little concrete progress has been achieved thus far, either with respect to possible cures or equally important on the front of understanding the causes that determine and regulate its course. Currently, the most widely followed research internationally are: (i) the genetic approach, which seeks to identify the gene or genes responsible for the illness for subsequent intervention through modern genetic engineering techniques; (ii) the transplant approach, an objective of which is to perfect a technique that would make it possible to transplant retinal tissue or, at least, graft healthy cells into diseased retinas; and (iii) the immunological approach, which develops and investigates theories that what underlies the illness is some alteration of the immunological system.